Bis(alpha-alkylbenzyl) ethers, such as bis(alpha-methylbenzyl) ether, have found application as dye carriers in the fabric industry, solvents in copying paper, and as direct substitutes for polychlorinated biphenyls in capacitors, and as heat transfer media, as well as components for use in the fragrance field. Certain of such ethers have also found use as pesticides, antioxidants, plastic additives and germicides. For example, Japanese Pat. No. 79-149900 has recently referred to the use of such ethers as electrical insulating oils and Japanese Pat. No. 79-136915 has referred to the use of such ethers in pressure-sensitive copying papers. The preparation of bis(alpha-alkylbenzyl) ethers by reaction of a suitable alpha-unsubstituted or substituted phenyl-alkanol in the presence of a dehydrating agent, such as sulfuric acid, benzene-sulfonic acid, toluene sulfonic acid, and camphor-sulfonic acid, thereby splitting out water and forming an ether linkage between the aliphatic carbon atoms of two molecules of the original alkanol compound has been reported in the literature, for example, in U.S. Pat. No. 2,366,203 and Journal of Organic Chemistry, 28, 2914-5 (1963). More recently, acidified alumina catalysts and ion exchange resins containing acidic functionalities have been suggested for use in the preparation of such ethers from the corresponding alkanols. However, these catalysts, as well as those originally reported for use in the etherification reaction, suffer a combination of shortcomings, including poor selectivity to the desired bis ether, poor reproducibility of results and high costs. In addition, it was necessary to employ such acid catalysts at high levels to be effective, thereby further increasing their costs, and to quench the catalyst quickly to avoid alteration of desired product selectivities. Furthermore, in many instances, it was not possible to satisfactorily quench the catalyst in situ and therefore purify product by distillation without first filtering the catalyst from the system. This inability to quench prior to product recovery made processing much more difficult to control and more expensive as both additional capital equipment and time would be required in recovery of the desired bis ether. The refining of alpha-alkylbenzyl ethers, such as alpha-methylbenzyl ether, by distillation, such as azeotropic distillation, has also been reported in U.S. Pat. No. 2,927,064.
In one prior process for producing alkylene oxides, e.g. propylene oxide and styrene monomer, ethylbenzene is oxidized with air in a series of oxidizers to yield a solution of ethylbenzene hydroperoxide in ethylbenzene. During this oxidation, substantial quantities of methylbenzyl alcohol and acetophenone by-products are formed. This solution of ethylbenzene hydroperoxide is then concentrated in successive steps of distillation, and unreacted ethylbenzene is recycled for oxidation. In this process, ethylbenzene hydroperoxide is then typically used to epoxidize the olefinically unsaturated compound e.g. propylene, to propylene oxide, in the presence of a suitable catalyst, and the hydroperoxide itself is converted to methylbenzyl alcohol. By-products of this reaction include additional quantities of acetophenone, phenol, benzaldehyde, 2-phenylethanol, unreacted reactants and high boiling materials.
Excess propylene in the aforementioned propylene oxide epoxidation product is normally removed by distillation and propylene oxide may then be recovered by distillation as a crude product, leaving a stream comprising excess ethylbenzene, the aforementioned by-products and residues. The stream is then distilled to recover ethylbenzene overheads, leaving an aromatic rich distilland comprising methylbenzyl alcohol, acetophenone and a variety of other by-products, including aromatic alcohols. The composition of such distilland may vary widely and comprises a variety of alcohols, ketones and other by-products, as set forth in Table I, below.
In a typical propylene-oxide styrene monomer production process, the aforementioned methylbenzyl alcohol/acetophenone distilland (bottom stream) is purified through distillation, and then is fed through styrene production reactors where it is contacted in a liquid phase with a suitable dehydration catalyst to convert methylbenzyl alcohol to styrene. After removing styrene from the dehydration reaction product by distillation, there is produced an acetophenone-rich bottoms product which is then hydrogenated using a suitable catalyst to convert acetophenone to methylbenzyl alcohol, which may then be recycled for styrene production or employed in alternative applications. Further information concerning the production of alpha-methylbenzyl alcohol from such processes is described in U.S. Pat. No. 3,403,193.
Accordingly, it is the object of the present invention to provide a novel process for the preparation of bis(alpha-alkylbenzyl) ethers.
Another object of this invention is to provide a process for the preparation of bis(alpha-alkylbenzyl) ethers from alpha-alkylbenzyl alcohols by employing a catalyst which provides high reproducibility and selectivity to the desired ether.
Still another object of the present invention is to provide a process employing an acid catalyst which need not be removed from the reaction product system prior to recovery of the ether product, thereby permitting production of the desired ether without employment of additional and expensive capital equipment.
Yet another object of the present invention involves the preparation of alpha-methylbenzyl ether from a crude methylbenzyl alcohol-containing stream obtained in olefin oxide-styrene monomer production processes.
These and other objects of the present invention will become apparent from the following more detailed description and appended claims.